在剪切应力场下少量HMWPE诱导HDPE的微观结构

采用少量高分子量聚乙烯(HMWPE)在动态保压剪切应力场中诱导中等分子量聚乙烯(MMWPE),在这种双重诱导的作用下得到了性能良好的聚乙烯材料,其平行于流动方向的拉伸强度和冲击强度达到了71.17 MPa和75.79 kJ/m<'2>,分别提高了209.4%和252.8%;通过差示扫描量热(DSC),X射线衍射(WAX...     

形态控制技术获取自增强制件研究

在成型过程中向成型设备或模具分别输入具有不同振频和振幅的振动场、不同拉伸比的拉伸应力场、不同剪切速率的剪应力场、以及先剪切后拉伸的复合应力场等,成功地改变了聚合物凝聚态结构;改变了结晶聚合物的结晶度、取向度、晶粒尺寸、晶胞参数;生成了不同的串晶结构、串晶互锁结构。分别得到了具有突出高强度、高模量的试样,自增强同时又自增韧的试样,在单方向应力场中获得双向自增强结构的试样,以及在极少量高分子组分诱导下性能大幅度提高的试样。     

低频振动场对HDPE性能的影响

利用低频熔体振动注射成型技术获得自增强高密度聚乙烯。实验结果表明,采用振动注射成型工艺,试样屈服拉伸强度由26.5MPa提高到36.1MPa;试样的芯层中可获取沿流动方向生成的串晶或行式排列的片晶结构;压力振动注射有利于分子在(110)晶面择优取向,使结晶更加完善;振动注射提高了试样的结晶度,芯层结晶度最大提高了10.2%。     

HDPE在少量HMWPE和剪切应力双重诱导作用下结构与性能的关系

将少量高分子量聚乙烯(HMWPE)和动态剪切应力场同时引入到高密度聚乙烯(HDPE)的注射成型过程中,在双重诱导的作用下制备了性能良好的聚合物材料,其拉伸强度和缺口冲击强度都有大幅度提高;同时通过形态表征(差示扫描量热、广角X射线衍射、扫描电子显微镜分析)对增强增韧的机理进行了探讨。     

聚乙烯增强增韧改性进展

论述刚性无机粒子、纳米材料、晶须、离聚体和聚酯短纤维对聚乙烯的增强增韧改性,以及聚乙烯的自增强增韧行为,并介绍改性聚乙烯的性能和改性机理。     

Adult Attachment, Depressive Symptoms, and Validation From Self Versus Others.

Attachment working models of self and others may govern adults' preferences for internal vs. external sources of reassurance, which, if unavailable, lead to depressive symptoms. This study examined a model in which the link between depressive symptoms and attachment anxiety is mediated by (a) capacity for self-reinforcement and (b) need for reassurance from others, whereas the link between depressive symptoms and attachment avoidance is mediated only by the capacity for self-reinforcement. Analysis of survey data from 425 undergraduates indicated that both capacity for self-reinforcement and need for reassurance from others partially mediated the link between attachment anxiety and depression. Capacity for self-reinforcement fully mediated the link between attachment avoidance and depression. Moreover, 54% of the variance in depressive symptoms was explained by attachment anxiety, self-reinforcement, and need for reassurance from others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple Structure Reconstruction by Dual Dynamic Crosslinking Strategy Inducing Self-Reinforcing and Toughening the Polyurethane/Nanocellulose Elastomers

High-performance elastomers are expected to possess excellent healing and recycling ability, damage resistance in conjunction with high strength and toughness. Herein, a dual dynamic crosslinking strategy is implemented by multiple hydrogen and disulfide bonds to obtain a novel amorphous and transparent polyurethane/nanocellulose elastomer with excellent self-healing, self-reinforcing and toughening performance. First, hydrogen bonds are introduced in TEMPO-oxidized cellulose nanofibers (TCNF) by modification with 2-ureido-4[1H]-pyrimidone (UTCNF), while disulfide bonds (SS) are introduced in the polyurethane (PU) main chain, leading to the formation of dual dynamic cross-linking networks. The PU-SS-UTCNF elastomer can fully self-heal within 4.0 h at 50 °C. Surprisingly, for the first time, the PU-SS-UTCNF elastomer also self-strengthens and self-toughens after multiple hot-pressing, with tensile strength and toughness that increase by up to 401% and 257% compared to original elastomer samples, up to 50.0 MPa and 132.5 MJ m^-3. The self-strength and self-toughening effects are attributed to 1) reconstruction of dual dynamic networks that increase the cross-linking degree during the multiple hot-pressing processes; 2) multiple hydrogen bonds in the system are beneficial to the orientation of highly crystallized UTCNF, as a replacement of stress-induced process in deformation under external tensile force.     

自增强HDPE棒材的结构及力学性能

通过扫描电子显微镜、差示扫描量热法、广角X射线衍射分析与力学性能测试,研究了自增强高密度聚乙烯(HDPE)棒材微观结构特点和力学性能。结果表明,自增强HDPE棒材呈现明显的皮芯结构,表皮的结晶度高达75．88％,芯部的组织和结构与普通注塑试样最相近;与普通HDPE试样相比,自增强HDPE棒材的微晶尺寸和结晶度大幅提高,晶面间距几乎未变化,内部存在大量的微纤结构。制备的自增强HDPE棒材的拉伸强度和弯曲强度分别为220．6 MPa和152．9 MPa,均为未增强试样的近10倍。     

A mandrel-rotating die to produce high-hoop-strength HDPE pipe by self-reinforcement

This article provides a method to obtain high-hoop-strength high-density polyethylene (HDPE) pipe by mandrel-rotating extrusion. With properly selected processing temperature, pressure, and mandrel-rotating speed, the hoop strength of 90 Mpa has been got. Differential scanning calorimetry and X-ray scattering found the great strength enhancement was owning to high degree of macromolecular orientation in circumferential direction and the shish-kebab structure. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 323–328, 1998     

木粉含量对连续固态挤出自增强PP性能的影响

采用单螺杆挤出机连续固态挤出制备自增强聚丙烯(PP)复合材料试样,对不同木粉含量的试样性能进行表征和综合分析。结果表明,PP复合材料试样密度随着木粉含量的增加呈线性上升趋势;拉伸强度和弯曲强度呈现先上升后下降的趋势,而在木粉含量为50%时达到最大;拉伸弹性模量和弯曲弹性模量随着木粉含量的增加一直增大,但断裂伸长率下降;木粉含量的增加能够提高试样的耐热性,但结晶度有所下降;木粉含量过多会造成复合材料界面结合减弱,影响最终复合材料的性能。